Are you getting "Unable to generate new address" error on checkout  or "error on Test Setup" on your E-Commerce store? Depending on the error that is showing, you may need to take one of the following actions: 

1.Error: "API Key is incorrect":  Make sure you have setup your API key correctly and that this field is not empty. Your APIKey is available on the Merchants Page. 

2. Error: "Your merchant account is disabled due to low balance": Check the "Upgrade" tab in your Blockonomics account. If your account is disabled, you can re-enable the account by sending Bitcoin (BTC) to the deposit address on the Upgrade Page

A Disabled Merchant account on upgrade page

3. Error: "You have not entered an xPub: Blockonomics needs  an extended public key(starting with xpub) so that it can generate new bitcoin address for each customer order. Visit Merchants - BTC, Merchants - BCH to see how to get xpub of your wallet. Please see this video on how to locate xpub of wallet

4. Error: "You have an existing callback URL. Refer instructions on integrating multiple websites": This means you have an another website callback pointing to your xpub. You need to add one more xpub to support multiple sites. Check this article for more detailed information  

5. Error: "Unable to locate/execute <your site> testsetup.php. Check your WHMCS System URL ":  Your WHMCS system URL path/domain is wrong, for example instead of using , you have specified . Thus Blockonomics is unable to locate the files